In many wireless communication systems, a mobile wireless device such as a cellular telephone, mobile internet device (MID), personal digital assistant (PDA), laptop, personal computer and so forth communicates wirelessly at a radio frequency (RF). To enable communication in a given wireless communication system, such devices are required to output an RF signal having a given power level. Different wireless systems have different requirements for power levels, and furthermore in a given communication system, power levels may vary depending on communication mode. To generate output power needed for transmitting information, typical mobile devices include a power amplifier (PA) or other such amplifier that receives RF signals from processing circuitry of the device, such as a baseband processor and transceiver or so forth, and amplifies this RF signal to a required power level.
Due to power control requirements in many transmitter systems, average output power can vary over a wide range, for example, several tens of decibels (dBs). This makes a power amplifier's efficiency change dramatically over the power range. Most PA's have maximum efficiency at maximum output power, and efficiency drops rapidly as power is reduced.